First data from the ATLAS Inner First data from the ATLAS Inner Detector FSI Alignment System Detector FSI Alignment System S. M. Gibson, P. A. Coe*, M. Dehchar, J. Fopma, D.F. Howell, R. B. Nickerson, G. Viehhauser KEK, Tsukuba, Japan. 15 February 2008. Particle Physics, University of Oxford, UK. *John Adams Institute for Accelerator Science ATLAS experiment, CERN.
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First data from the ATLAS Inner First data from the ATLAS Inner Detector FSI Alignment SystemDetector FSI Alignment System
S. M. Gibson, P. A. Coe*, M. Dehchar, J. Fopma, D.F. Howell, R. B. Nickerson, G. Viehhauser
KEK, Tsukuba, Japan.15 February 2008.
Particle Physics, University of Oxford, UK.*John Adams Institute for Accelerator Science
ATLAS experiment, CERN.
Gibson et al. First data from the ATLAS inner detector FSI alignment system 2
Overview• Motivation
– ATLAS ID alignment
• Frequency Scanning Interferometry– On-detector grids.– Reminder of technique – System Overview
Gibson et al. First data from the ATLAS inner detector FSI alignment system 19
Two colour laser amplifier system
Gibson et al. First data from the ATLAS inner detector FSI alignment system 20
Two colour laser amplifier system
Phase locked choppers so only one laser illuminates system at any time
Gibson et al. First data from the ATLAS inner detector FSI alignment system 21
0
200
400
600
800
1000
1200
1400
1600
1800
2000
-7000 -6000 -5000 -4000 -3000 -2000 -1000
Laser Frequency /a.u.
Inte
nsity
/ a.
u.
Interferometer signal10 GHz Etalon
Frequency scanning with new system140 GHz mode hop free tuning
Gibson et al. First data from the ATLAS inner detector FSI alignment system 22
170.420
170.422
170.424
170.426
170.428
170.430
170.432
170.434
170.436
22.90 22.95 23.00 23.05
Invar interferometer temperature / degrees
Mea
sure
d le
ngth
/ m
m
Subscan ASubscan BLinked
Preliminary Results (2nm link)
σ= 96nmresolution
Gibson et al. First data from the ATLAS inner detector FSI alignment system 23
RISRIS Vacuum chamber
This vacuum chamber houses theRReference IInterferometry SSystem:all grid lengths measured with respect to this stable reference interferometer length.
Why use a vacuum? 1. Reduces errors due to pressure differences between laser room / ATLAS cavern.2. Eliminates systematic drift during scan due to refractive index changes / turbulence3. Thermally isolates reference from surroundings to reduce changes in length.
Gibson et al. First data from the ATLAS inner detector FSI alignment system 24
design to balance CTEs. ΔT(C1 L1 – C2 L2 ) = 0.• Both interferometers have four-fibre read-out
for instantaneous phase measurement.• Long reference has piezo for phase stepping.
Super-invar rods
launch collimators
Gibson et al. First data from the ATLAS inner detector FSI alignment system 25
Vernier etalons• The vacuum chamber contains
a pair of Fabry Perot etalons with slightly different Free Spectral Ranges:10.00GHz and 10.05Gz
• Each etalon produces a comb of peaks as the frequency is scanned.
• The FSRs were chosen to provide a beat pattern repeating over 2010GHz (Repeat cycle = N2 FSR-1 = N1 FSR2)
• This vernier scale allows frequency intervals between sub scans to be determined.
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(Short) Reference Interferometer
Laser light enters via fibre collimator held in a 4-axis manipulator.
Short arm
Long arm mirror
Read-out by 4 parallel ribbon fibres
Gibson et al. First data from the ATLAS inner detector FSI alignment system 27
Phase stepping of piezo mounted mirror
Phase extractionand unwrapping
FINE-TUNING CURVE
0 40 80 120 160 200 240
-2000
0
2000
Unwrapped Reference Phase
Φ
/ rad
Time / s
Laser 1
Laser 2
Phase extracted from RI intensity at 4 step positions of mirror.
Limitations • Four DAQ cycles are required for each phase measurement.• DAQ rate is limited by maximum driving frequency of the piezo.
PD
Main Reference Interferometer
Piezomounted
mirror NBS
PinholeReference Interferometer phase steps
Gibson et al. First data from the ATLAS inner detector FSI alignment system 28
New: Four-fibre phase extraction
Phase extractionand unwrapping
Four interference signals coupled simultaneously into four parallel fibres
Advantages of new method:• Instantaneous phase measurement.• Not limited by piezo vibration rate.• Permits much faster frequency scans.
This reduces interferometer drift errorsand improves the measurement precision.
Laser 2
Laser 1
Gibson et al. First data from the ATLAS inner detector FSI alignment system 29
Very new: Dual interferometer phase extraction
LR four fibre phase extractionShort interferometer
Long interferometer
SR four fibre phase extraction
Long Reference Short ReferenceInterferometerintensity vs time
Extracted phase vs Time
Phase residualsvs Time
(non-linear laser frequency scan)
LR residuals SR residualsΔϑ = [2π/c]DΔνΔΦ = [2π/c]LΔν
Directly measurephase in both RIs
Gibson et al. First data from the ATLAS inner detector FSI alignment system 30
Very new: Direct length ratio measurementS
hort
inte
rfero
met
er p
hase
, Δϑ
Long interferometer phase, ΔΦ
Residuals from straight line fit [mode hop free region]
Δϑ = [2π/c]DΔν
ΔΦ = [2π/c]LΔνΔϑ/ΔΦ
= D/L
Length ratio = gradient
0.215516
0.215520
0.215524
0.215528
0.215532
0.215536
24 29 34 39
Repeat for 15 subscans:
SR/LR length ratio, D/L =0.2155274 +/- 0.000003
Equivalent to 3 μm on SR length.Δν currently limited by laser mode hops.
D/L
Preliminary result:(single laser only, short range Δν=34 GHz)
Gibson et al. First data from the ATLAS inner detector FSI alignment system 31
Light distributionand
Read out
Gibson et al. First data from the ATLAS inner detector FSI alignment system 32
Control and data acquisition• 2 VME crates
– Laser room: Control crate • control of lasers• 2 FROCs: for inteferometers, etalons,
diagnostics + vacuum chamber pressure, temperature measurements.
– USA15: Readout Crate • readout of 842 GLIs
• Optical link between crates to synchronise DAQ.
• Optical link runs in same ribbon cable as fibre delivering high power laser light to rack.
• Laser light is divided between 842 interferometers using a fibre splitter tree, based on Planar Lightwave Circuits.
• DAQ uses custom FSI Read Out Cards (FROCs), which each record 64 optical channels multiplexed to 32 electronic channels.
Gibson et al. First data from the ATLAS inner detector FSI alignment system 33
Commissioning the FSI Read-Out Cards• 2006: cables to empty rack.• June ‘07: Crate,and first FROC
installed. Communication established via SBC.
• August ‘07 shipment: 6 FROCs + CNC card installed. Block transfer achieved.
• October ‘07 shipment: all 15 FROCs installed. Full data rate test successful: 65536 triggers (~4.5Mb per FROC).
8
8.2
8.4
8.6
8.8
9
9.2
9.4
9.6
9.8
10
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
slot
data
rate
[MB/
s]
13th FROC (!) had a broken trace in the multilayer board. Repaired in Oxford, now back at CERN
Gibson et al. First data from the ATLAS inner detector FSI alignment system 34
Fibre Splitter Tree Installation• Purpose – to split fibre coupled laser light between 842 interferometers.• Tree built using Planar Lightwave Circuit technology (PLCs) rather than
fused biconic couplers.• Fibre-like waveguides created using ion-exchange in glass.
– 1x8, 1x16, 1x32 split multiplicity possible in single device.• Need far fewer devices with similar / better optical losses to couplers.• Compact form allows easier installation at rack.
– PLC chip was mode matched to specialist radiation tolerant ribbon fibre to reduce splice losses.– Splitter tree made in 15 x 1U modules of fibre mixing matrices manufactured in Oxford over summer and shipped to CERN, in August and October. [1684 individual fibres routed].
Gibson et al. First data from the ATLAS inner detector FSI alignment system 35
Splitter tree modules in underground rack
• 9 x 1U splitter tree modules installed on sliding runners at the rack.
• Each module divides fibre coupled light from the lasers between up to 64 grid line interferometers on the SCT, and routes the return light to the read-out crate (one FROC per splitter module).
Gibson et al. First data from the ATLAS inner detector FSI alignment system 36
Splitter tree module in counting room rack
SCT ribbons
APD read outribbons
PLC splitters Fibre mixing matrix
Gibson et al. First data from the ATLAS inner detector FSI alignment system 37
Status and outlook• The FSI system is in place at CERN and the commissioning phase has
started.• Read-out system tested successfully with fast data transfer rate achieved.• Four-fibre phase extraction technique developed to improve precision.• Dual reference interferometers provide simultaneous phase extraction.• First data indicate improved performance is possible using extended
analysis techniques and frequency tuning capabilities of the new lasers.
Acknowledgements:• Special thanks to technical staff from Oxford Physics Central Electronics and
Mechanical Group, in particular: J. Brown, C. Evans, B. Finegan, F. Gannaway, M. Dawson, T. Handford, G. Hammett, M. Jones, P Lau, W. Lau, J. Lynn, R. Makin, R. Morton, M. Newport, L. Rainbow, R. Swift, M. Tacon.